Flowable plastic materials are commonly used in manufacturing processes as sealants and adhesives. For example, a single component polyurethane adhesive-sealer is commonly applied around the periphery of windshield glass to provide a sealant and adhesive. The material is applied as a bead. The commonly used polyurethanes cure at room temperature to a rubber-like consistency. The curing is caused by reaction with moisture in the air.
The plastic material is frequently dispensed as a bead from automatic dispensing machinery. Such dispensing machinery employs a nozzle-like dispensing tip connected to a plastic material source. During usage of the dispensing machinery, material is purged frequently enough to prevent hardening of the material in the dispensing tip and the area rearward thereto. However, during periods of non-use, such as may occur overnight, on weekends, during plant shut-downs and the like, material is not dispensed from the dispenser tips. If material is not frequently dispensed from the dispenser tip, it can harden in the passage of the dispenser tip and plug the dispenser tip and perhaps passageways therebehind. In order to prevent this from occurring, the dispenser tip has been purged at regular intervals during periods of non-use by forcing plastic material therethrough even though the material is not used. This material is lost by dumping it into a drum or other container. This is, of course, an expensive proposition.
In accordance with the present invention, a method is provided to prevent hardening of the plastic material during periods of non-use of dispensing machinery.